Is there anyway besides purchasing a new OS X Tiger to refresh his computer so he is able to sell it without his personal information being on the machine?
If it is a newer Intel machine, the standard Tiger OS Retail Box won't work.
The OS X Retail Boxes typically only boot machine made before the OS release, about April 2005 or older.
If you lost the DVDs for a newer machine, call Apple and see if they will send you out a new set of DVDs for a lost/damaged set -- probably about $19.95, haven't checked in a long while.
I suppose he could have the reciept that shows he paid for it and he could go to an Apple Store and beg and plead and offer his firstborn and maybe the folks might consider reloading Tiger onto it (if it is new enough a machine to have come with Tiger). Otherwise...well...nope.